Power Output
Training

by Edmund R.
Burke, Ph.D.

Just as training methods changed with the advent
of portable heart rate monitors, power meters are pushing the theories and
methodology of endurance training into new territory. The biofeedback that
power meters provide brings amazing clarity to training, if the information is
interpreted well. Speed, perceived effort, and heart rate are very useful for
gaining insight into a person's training, but variables associated with those
measures lead to ambiguous results under certain conditions.

In cycling, power is expressed as "Watts". Power
is the rate of work being completed. If you move from one point to another,
against the resistance of rolling friction, gravity, and/or aerodynamic drag,
you will do a certain amount of work. How fast you do that work is called
power. Work is defined as the product Force times Distance. If you lift or move
a 5-kilogram weight (1 kg = 2.2 pounds) over a 2 meter distance you would
perform 10 kg meters of work, or 10 kgm.

Power = Work divided by Time. One Watt is defined
as 6.12 kgm per minute or 0.102 kgm per second. Given enough time on the bike
any cyclist could complete 2,000 kgm of work. However, only a few highly
trained cyclists could perform that work in 60 seconds. Which would equal 33.33
kgm per second or 327 Watts. If several months latter they complete the task in
55 seconds they would be producing 356 Watts. They are now more powerful.

So, for example, if you climb to the top of a
hill you'll do a lot of work. The work it takes to get to the top of that hill
will be the same no matter how fast or slow you climb. However, if you climb
that hill twice as fast as the time before, you'll have exerted twice the
amount of average power as the time before. You can increase power by either
increasing your cadence, gear or by pushing harder on the pedals while riding
your bike. In terms of useful cycling information, power is much more valuable
than speed and distance. Variations in speed are difficult to evaluate. In
fact, maintaining a certain average speed may be an inefficient use of energy,
especially if one does not know the power required to maintain that speed. From
the power calculation you get an accurate picture of how efficient your body is
performing. Whether racing or training, you can compare one ride to another
using power as the basis.

Why Power and Heart Rate Training?

So how does the added element of power monitoring
play into training? Power output does not replace heart-rate measurement, but
is intended to be used in conjunction with it. The main benefit is that it
allows you to actually measure workload rather than make a guess at it based
soley on heart rate, which can be affected by temperature (heat or cold) and
other factors. Within any given ride you can easily evaluate performance based
on power output. At any point in the ride you can know if they are performing
at, below or above previous best performance.

Focus on power for intervals, hill training,
sprint training, and all anaerobic workouts. Often in these efforts heart rate
lags behind the intensity and the resulting change in heart rate. For example,
at the start of an interval, heart rate takes several seconds, or even minutes
to catch up with energy demands being expended. During a short sprint it will
never give an accurate measurement of the effort.

Heart rate along with power is best used for
steady state training, particularly that done below the lactate threshold. It
is especially effective during long, aerobic rides and for recovery workouts.
For training or racing, you can compare one ride to another by measured power
and heart rate. Within any given ride you can easily evaluate performance based
on power output. At any point in the ride they can know if you are performing
at, below or above previous best performance. Applying each of these intensity
monitoring systems has the potential to dramatically improve training and
racing. While using a heart rate/power system you will see significant
improvement in race performance when you begin training with power.

Training With Power and Heart Rate

One can now base endurance or aerobic workouts on
power levels and heart rate zones. If you are making the same power at a lower
heart rate than during previous endurance efforts over the same terrain, you
can measurably tell that your fitness has improved. Likewise, if you're making
less power at the same or higher heart rate, it is a sign you are losing
fitness. What if your heart rate is higher than normal, but you can't ride at
your target power output? Incomplete recovery from previous workouts is likely
to blame. Also, you can monitor recovery time from an effort of a certain
intensity, like during intervals. Equal power output followed by a more quickly
dropping heart-rate shows improved fitness. Combine this information with
distance, speed, cadence and other information and you have a complete training
monitor.

Power is the new kid on the block to help you
more accurately measure cycling intensity. Along with heart rate it accurately
measures your performance and helps prevent you from overtraining and under
training.